Yeah, we need to know what you're using the PC for. For loads of 3D work, and video editing the i7 is the only way to go, if gaming it's a waste of money.
Hyper Threading (HT) does nothing for games in case you did not know.
I don't think Haswell will have more than a 10% performance increase over Ivy Bridge; assuming the same clockspeed. I believe the real increase in perform will come with Broadwell. That's based on the assumption that Intel is focusing more on lowering power consumption (to penetrate the mobile device market), than increasing performance. Broadwell will get the 14nm die shrink so they those CPUs can provided increased performance while maintaining low power consumption.
I will be gaming and rendering and little 3d work later......
Also should I get the 3570k now and upgrade at broadwell or i7 now and upgrade at skylark.
I would get the 3570k, you said "little" 3d work, and little is not really justifiable to spend an additional $100 dollars. If 3d work and rendering was a normal thing for you then the 3770k would make more sense and the additional $100 would be put to good use.